<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <div class="vh">
    <h1>
font-size 20vh
    </h1>
  </div>
</body>
</html>
    html {height: 100%;}
    body {height: 50%;}
    .vh {height: 100vh;background-color:#eeddff}
h1 {
  margin: 0;
  font-size: 20vh;
}

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